It is well known that polymethylsilsesquioxane is a polymer comprising methylsilsesquioxane units which are trifunctional organosilicon units and can take a fine powder form. One of the present inventors previously found a method for the preparation of a polymethylsilsesquioxane fine powder suitable as a material for electronic parts and an additive for polymers as disclosed in JP-A- No. 63-77940 and JP-A- No. 63-295637 (the term "JP-A" herein used means an "unexamined published Japanese patent application").
Such a silicone resin fine powder comprising methylsilsesquioxane units is made of minute spherical particles usually having a particle diameter of about 0.05 to 100 .mu.m, and has advantages over silica in having a smaller specific gravity and better slip properties and being excellent in dispersibility into organic resins and organic liquids.
In preparing marine paints using a polymethylsilsesquioxane fine powder as a filler, since the polymer has no physiologically active group in its molecule, a proper conventional means should be taken to counterbalance it. For example, a (meth)acrylate-type polymeric compound in which a hydrolyzable triorganotin group has been incorporated at a side chain is used as a vehicle, or an organotin compound is incorporated into the paints as an antifouling agent. The use of such marine paints had a problem that the sea was contaminated by tin compounds.
As examples of treatment of an inorganic powder with a quaternary ammonium group-containing organosilicon compound, there are a technique of treating silica, alumina, zirconium dioxide or titanium dioxide to produce an anion exchanger as disclosed in, for example, JP-A- No. 56-105757, and a technique of treating glass beads or silica to prepare a germicide as disclosed in, for example, JP-A- No. 61-15804. However, application of the treatment with the above-described organosilicon compound to a polyorganosilsesquioxane fine powder is not known.